"Is track and field really a professional sport? For Usain Bolt, it is. A Forbes magazine survey released this month estimated the Jamaican sprinter's annual earnings at $23.2 million, ranking 45th on a list of the world's richest athletes. What about Kind Butler III? He is a world record-holder, too, albeit in a relay. The Indianapolis sprinter estimated his 2013 earnings from track: $6,000, or about 4,000 times less than Bolt. That underscores a challenge facing American athletes and their Indianapolis-based governing body, USA Track & Field."